1. Technical Field
Example embodiments of the present invention relates in general to a distributed video decoder and a distributed video decoding method.
2. Description of the Related Art
Video compression standards such as MPEG-4 video coding and MPEG-4 AVC/H.264 are usually employed in video players, video on demands (VODs), video telephones, digital multimedia broadcasting (DMB), and wireless mobile environments for video data compression and transmission. The compression techniques remove temporal redundancy to achieve high coding efficiency. A motion estimation and compensation technique is commonly used as a representative method of reducing temporal redundancy. However, the motion estimation and compensation technique has a disadvantage in that power consumption is high since computation cost of a moving picture encoder is relatively high. Therefore, in order to achieve low power consumption, it is very important to reduce complexity of the encoder in a limited source environment such as a sensor network.
As a method of resolving the complexity problem of the encoder, a distributed video coding (DVC) technique which is based on a Wyner-Ziv theorem has been highlighted. The distributed video coding technique separately encodes video pictures and does not perform motion compensation between video pictures, which is performed in existing techniques, in order to detect similarity between video pictures, whereby computation cost is reduced.
A conventional distributed video coding technique based on the Wyner-Ziv theorem will be described below with reference to FIG. 1. FIG. 1 is a block diagram illustrating a configuration of an encoder 110 and a decoder 130 according to a conventional Wyner-Ziv coding technique.
The encoder 110 classifies pictures of a source video content into two types. One is a picture (hereinafter, referred to as a “WZ picture”) which is to be encoded by the distributed video coding technique, and the other is a picture (hereinafter, referred to as a “key picture”) which is to be encoded by a conventional coding technique other than the distributed video coding technique.
The key pictures are encoded in a key picture encoding unit 114 by, for example, an intra picture coding technique of H.264/MPEG-4 AVC and transmitted to the decoder 130. A key picture decoder 133 of the decoder 130 reconstructs the received key pictures. A side information generating unit 134 generates side information corresponding to the WZ picture using the key pictures reconstructed by the key picture decoding unit 133 and transmits the side information to a channel code decoding unit 131.
The side information generating unit 134 assumes a linear motion between pictures located before and after the WZ picture and generates the side information corresponding to the WZ picture by using an interpolation technique.
In order to encode the WZ picture, a quantization unit 111 of the encoder 110 performs quantization of the WZ picture and outputs quantized values of the WZ picture to a block unit dividing unit 112. The block unit dividing unit 112 divides the quantized values of the WZ picture into predetermined coding units. A channel code encoding unit 113 generates a parity bit of each coding unit by using a channel code.
The parity bits are temporarily stored in a parity buffer (not illustrated) and then sequentially transmitted to the decoder 130 when the decoder 130 requests the parity via a feedback channel.
The channel code decoding unit 131 of the decoder 130 receives the parity from the encoder 110 to estimate the quantized values. A video reconstruction unit 132 receives the quantized values estimated by the channel code decoding unit 131 and dequantizes the quantized values to reconstruct the WZ picture.
The distributed video coding technique based on the Wyner-Ziv theorem corrects a noise included in the side information generated by the decoder by using the parity and thereby reconstructs the current WZ picture. As the noise included in the side information is decreased, a required parity amount is decreased. Therefore, in order to have a good rate-distortion performance, it is important to generate the side information without a noise. The side information is typically generated such that a motion vector between reconstructed key pictures is estimated, a motion vector of side information which is desired to be reconstructed is obtained from the motion vector between the reconstructed key pictures in consideration of a distance between the pictures, and a coding unit within a key picture indicated by the obtained motion vector of the side information is generated as the side information.
FIG. 2 illustrates a conventional method of generating the side information. A motion vector MV2 of side information to be reconstructed is obtained from a motion vector MV1 between reconstructed key pictures. It can be understood that the motion vector MV2 of the side information is half (½) of the motion vector MV1 between the key pictures. Of course, there may be several side information between pictures, and a motion vector between key pictures may be obtained from both directions.
However, in the case in which the motion vector of the side information which is desired to be generated is obtained from the motion vector between the reconstructed key pictures, when a motion between pictures is complicated, when a motion does not linearly change, or when an object or a background suddenly disappears or appears, wrong side information may be generated. In this case, since the generated side information has a lot of noises, it is difficult to sufficiently remove the noises by the received parity.
For the foregoing reasons, information (hash information) of the WZ picture is necessary. The hash information is useful in generating the side information without any noise, but the hash information itself has a large amount of bits, and thus there is a problem in that a transmission bit rate is increased. Therefore, there is a need for improving the quality of the side information from which the noise is difficult to be removed while reducing an amount of bits increased by the hash information.